Our project involves the development of new techniques to study the conformation of histone and non-histone proteins within chromatin. We have employed lactoperoxidase-catalyzed iodination techniques to label tyrosyl residues of histone and non-histone proteins within the chromatin strands, and have observed differences between experimental (enzyme-catalyzed) and control (chemically-catalyzed) iodination patterns of the histone proteins. In addition, we have prepared a fluorescent probe, n-pyrene-maleimide, to label specifically the cysteinyl residue of histone H3 within rat liver and chick erythrocyte chromatin with high efficiency. Terbium, a lanthanide element which fluorescences when bound to DNA, is also being employed to study DNA accessibility within nuclei, chromatin, and nucleosomes. When the conditions of labelling for such probes is established, we will employ them to investigate changes in DNA-histone and DNA-non-histone protein interactions within chromatin and nuclei from both leukemic lymphocytes in the AKR mouse and erythroleukemic erythroblasts in the chick (obtained by prior infection with an erythroblastosis virus). Hopefully, the use of such biophysical techniques will enable us to obtain some idea at the molecular level of changes occurring in the nucleus following leukemogenesis.